In general, signal processing refers to techniques and processes by which analog and digital signals are created, transmitted, received, and interpreted, among other functions. In many instances, the signals are electromagnetic signals that are processed using various electrical devices and circuits, some of which are known as receivers. When the signals that are being received are radio-frequency (RF) signals, the receivers are known as RF receivers, which often have an antenna structure connected to what is known as the front end of the receiver, the front end in turn being connected to a demodulation stage.
Two types of RF receivers are those known as voltage-mode RF receivers and current-mode RF receivers. More generally, various circuit components (i.e., elements) can be realized as either voltage-mode components or as current-mode components. In voltage-mode receivers and components, the information of a given signal is represented in the voltage domain (as a set of nodal voltages of a given circuit). In current-mode receivers and components, the information of a given signal is represented in the current domain (as a set of branch currents of a given circuit).
Furthermore, electromagnetic signals have various characteristic properties, one of which is frequency, which is typically expressed in Hertz (Hz) or a standard multiple thereof such as kilohertz (kHz), megahertz (MHz), gigahertz (GHz), and the like. Signals are often categorized by frequency into defined ranges, two common examples being RF signals and baseband signals. RF signals are typically defined as signals having frequencies in a range of a few MHz to about 300 GHz, some representative examples that are used in communications being 800 MHz, 1900 MHz, and 2.4 GHz, among many other examples. Baseband signals are typically defined as signals having frequencies ranging from 0 (zero) Hz to the modulation bandwidth of the received signal. Another category, which is often referred to as “intermediate signals,” is typically generally defined as signals having frequencies that lie between those of RF signals and those of baseband signals. Moreover, terms such as baseband signals (and baseband frequencies), intermediate signals (and intermediate frequencies), RF signals (and RF frequencies), and the like, are known to those having skill in the art; as such, the above definitions should be taken as being illustrative and not as limiting any such terms to any specific numerical values.
Furthermore, as is also known to those of skill in the art, a signal in a given category (i.e., a signal that has a frequency that falls within the given category) can be converted into a signal in another category (i.e., into a signal that has a frequency that falls within the other category). In the context of a given receiver, the front end typically carries out this process, which is often called frequency translation. Many RF receivers operate such that they convert received RF signals into intermediate signals, and then in turn convert those intermediate signals into baseband signals, which are generally considered to be more feasible and practical to process (e.g., demodulate) than are signals at (the higher) intermediate and RF frequencies. Other RF receivers are arranged to perform what is known as direct conversion, whereby RF signals are converted directly into baseband signals. Such RF receivers are often referred to as direct-conversion RF receivers.
As is further known to those of skill in the art, a given receiver may receive a signal that includes a number of different signals, referred to at times herein as component signals, at a number of different frequencies. The difference between the highest frequency and the lowest frequency among the various frequencies of the component signals is known as the bandwidth of the received signal, indicating how much of the electromagnetic spectrum is spanned by that signal. Signals that have relatively large bandwidths are often referred to as being wideband, while signals that have relatively small bandwidths are often referred to as being narrowband.
In operation, and among other functions, a direct-conversion RF receiver, whether it be a current-mode receiver or a voltage-mode receiver, that is tuned to what is known in the art as a channel of interest typically (i) receives a wideband RF signal that includes the channel of interest and (ii) outputs to its demodulation stage a narrowband baseband voltage signal that contains essentially only the channel of interest. Indeed, that narrowband baseband voltage signal typically has a bandwidth that ranges from a few kHz to the tens of MHz, spanning the channel of interest.
If a potentially interfering signal is present in the RF environment at a frequency outside of that narrow band, the receiver may experience what is known as front-end compression—reducing the likelihood of reliably receiving and decoding the channel of interest—without knowing (i.e., without being able to detect, respond to, correct for, and the like) the cause of such compression. To address this issue as well as others, the present systems and methods use a mirrored wideband baseband current for automatic gain control of an RF receiver.
Those having skill in the relevant art will appreciate that elements in the figures are illustrated for simplicity and clarity, and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments. Furthermore, the apparatus and method components have been represented where appropriate by conventional symbols in the figures, showing only those specific details that are pertinent to understanding the disclosed embodiments so as not to obscure the disclosure with details that will be readily apparent to those having skill in the relevant art having the benefit of this description.